We have undertaken the following experiment in order to investigate the effect of the Hydrazide for leprosy from May, 1952. We selected the 20 lepromatous leprosy who had not ever received any treatment for leprosy. The way of administration were as following : at first we gave them 1mg/kg per os and then after one month gave them 5 or 6mg/kg. The results were summarized as following : 1. The resorption of nodules and infiltrations were observed in 13 patients (65%)after 4 or 6 months, but when they more over continued this treatment we found relaps of leproma in 12 patients after 2 months. 2. We also observed this finding in the histological and bacteriological examination of skin, nasal mucous membrane and blood. 3. This new leproms were resorbed by promin treatment within 2 or 3 months. 4. Erythema nodosum leprosum was observed in only 2 cases (10%). 5. Mitsudas reaction showed no change. 6. Liver and kidney function test showed no change. 7. On second function we could not experiment any important complcation. 8. Lepra bacilli of skin and nasal mucous membrane after 5 months decreased a little but later had a tendency to increase. 9. On blood findings we observed that erythrocytes and hemoglobin decrease a little and lymphocyte and eosinophile cell increase but neutrophile leucoytes decrease. 10. Result in total I. Improvement 13 cases (68%) a. Improvent 1 case (8%) b. Relaps 12 cases (92%) II. Worse 6 cases (30%) III. Stationary 1 case (5%) In short this observation is carried out 10 months in our experiment which leads to the following concusion : Hydrazide is effective for lepromatous leprosy after 4 or 6 months but relaps occur before long (about after 2 months, ).